1. Technical Field of the Invention
The present invention generally relates to signaling server timing distribution. More particularly, and not by way of any limitation, the present invention is directed to a method and system for embedding the phase of a first clock signal within a second signal.
2. Description of Related Art
Out-of-band signaling establishes a separate channel for the exchange of signaling information between call component nodes in order to set up, maintain, and service a call in a telecommunications network. Such channels, called signaling links, are used to carry all of the necessary signaling messages between the nodes. Thus, for example, when a call is placed, the dialed digits, trunk selected, and other pertinent information are sent between network switches using their signaling links, rather than the trunks that will ultimately carry the bearer traffic.
Out-of-band signaling has several advantages that make it more desirable than traditional in-band signaling. First, it allows for the transport of more data at higher speeds than multi-frequency (“MF”) outpulsing used in the telecommunications networks of yore. Also, because of separate trunks and links, signaling can be performed at any time during the duration of the call, not just at the beginning. Furthermore, out-of-band signaling enables signaling to network elements to which there is no direct trunk connection.
SS7 packet signaling has become the out-of-band signaling scheme of choice between telecommunications networks and between network elements worldwide. Three essential components are defined in a signaling network based on SS7 architecture. Signal Switching Points (“SSPs”) are basically telephone switches equipped with SS7-capable software that terminate signaling links. They generally originate, terminate, or switch calls. Signal Transfer Points (“STPs”) are the packet switches of the SS7 network. In addition to certain specialized functions, they receive and route incoming signaling messages toward their proper destination. Finally, Signal Control Points (“SCPs”) are databases that provide information necessary for advanced call processing and Service Logic execution.
As is well known, SS7 signaling architecture is governed by several multi-layered protocols standardized under the American National Standards Institute (“ANSI”) and the International Telecommunications Union (“ITU”) to operate as the common “glue” that binds the ubiquitous autonomous networks together so as to provide a “one network” feel that telephone subscribers have come to expect.
The exponential increase in the number of local telephone lines, mobile subscribers, pagers, fax machines, and other data devices (e.g., computers, information appliances, etc.), coupled with deregulation that is occurring worldwide today is driving demand for small form factor, high capacity STPs that must be easy to maintain, provide full SS7 functionality with so-called “five nines” operational availability (i.e., 99.999% uptime) and provide the capability to support future functionality or features as the need arises. Further, as the subscriber demand for more service options proliferates, an evolution is taking place to integrate Intelligent Network (“IN”) capable SCP functionality within STP nodes.
While it is generally expected that a signal platform that supports large database/high transaction IN services as well as high capacity packet switching (hereinafter referred to as a “signaling server platform”) will reduce equipment costs, network facility costs, and other associated costs, while increasing economic efficiency, those skilled in the art will readily recognize that several difficulties must be overcome in order to integrate the requisite functionalities into a suitable network element that satisfies the stringent performance criteria required of telecommunications equipment. Daunting challenges arise in designing a compact enough form factor that is efficiently scalable, ruggedized, and modularized for easy maintenance, yet must house an extraordinary constellation of complex electronic circuitry, e.g., processors, control components, timing modules, I/O devices, line interface cards that couple to telecommunications networks, etc., that is typically required for achieving the necessary network element functionality. Whereas the electronic components may themselves be miniaturized and modularized into cards or boards, interconnecting a large number of such cards via suitable bus systems and controlling such interconnected systems poses many obstacles, especially in light of the stringent form factor requirements of the state-of-the-art equipment.
In addition, beyond the physical difficulties relating to maintenance, card replacement and repair, etc., providing tightly controlled internal clock signals (i.e., telecommunications clocks) in a reliable manner to the cards for synchronization (which is an essential aspect of the operation of a telecommunications switching/routing device) becomes a formidable task in the state-of-the-art solutions when a highly scalable architecture is required.
It should therefore be appreciated that the increasing growth of telecommunications networks has led to the demand for an improved method and system for distributing signals in a telecommunications network. Telecommunication systems distribute signals through a network to control and monitor the modules of the network. Signals distributed downstream include control commands for the downstream modules, while signals collected from the downstream modules include information about the status of the downstream modules. Telecommunications systems also distribute timing signals to synchronize the signals of a network. Telecommunication systems transmit high-speed data and therefore require dependable timing signals.
For error-free transfer of DS0 data between two telecommunications devices located at a site, industry standards require that the data transmission circuitry of each device use a raw, unfiltered, 64 KHz composite clock signal from a building integrated timing source (“BITS”) to define the data bit edges. Since each DS0 device uses this clock to recover data received from other DS0 devices, each DS0 device's transmit data must be appropriately aligned to the composite clock's 8 KHz frame. Furthermore, the device's central clock must not filter the composite clock wander and transients, but must follow them so that clock-to-data skew is minimized at the devices. On the other hand, if this same unfiltered clock signal is used to transmit data to or operate non-DS0 circuitry within other devices, the erratic nature of the composite clock can cause timing hazards and corrupt data in those circuits.
It is possible that a single system will include circuitry having different timing requirements. For example, a signaling server such as that described in above-referenced, commonly-assigned U.S. patent application Ser. No. 09/541,000, entitled “CLOCK DISTRIBUTION SCHEME IN A SIGNALING SERVER”, may accommodate both phase-dependent (e.g., DS0) links as well as non-phase-dependent (e.g., DS1, T-1, SONET) links. This can be accomplished by providing within the system two separate timing distribution mechanisms, one for the phase-dependent links and an other for the non-phase-dependent links. Such duplication clearly adds complexity both to cabling and circuitry requirements of the system, as well as increasing the associated software overhead involved in configuring and monitoring the timing distribution mechanism. Moreover, increasingly stringent space-limitations on system packaging standards require that the number of signals and cables in a system be minimized.
Accordingly, it would be desirable to implement a single timing distribution mechanism to distribute clock signals throughout the entire system. The prior art provides no means by which to accomplish this.